terms.object              package:base              R Documentation

_D_e_s_c_r_i_p_t_i_o_n _o_f _T_e_r_m_s _O_b_j_e_c_t_s

_D_e_s_c_r_i_p_t_i_o_n:

     An object of class 'terms' holds information about a model. 
     Usually the model was specified in terms of a 'formula' and that
     formula was used to determine the terms object.

_V_a_l_u_e:

     The object itself is simply the formula supplied to the call of
     'terms.formula'.  The object has a number of attributes and they
     are used to construct the model frame:

 factors: A matrix of variables by terms showing which variables appear
          in which terms. The entries are 0 if the variable does not
          occur in the term, 1 if it does occur and should be coded by
          contrasts, and 2 if it occurs and should be coded via dummy
          variables for all levels (as when an intercept or lower-order
          term is missing).

term.labels: A character vector containing the labels for each of the
          terms in the model.  Non-syntactic names will be quoted by
          backticks.

variables: A call to 'list' of the variables in the model.

intercept: Either 0, indicating no intercept is to be fit, or 1
          indicating that an intercept is to be fit.

   order: A vector of the same length as 'term.labels' indicating the
          order of interaction for each term 

response: The index of the variable (in variables) of the response (the
          left hand side of the formula).

  offset: If the model contains 'offset' terms there is an 'offset'
          attribute indicating which terms are offsets

specials: If the 'specials' argument was given to 'terms.formula' there
          is a 'specials' attribute, a list of vectors indicating the
          terms that contain these special functions.


     The object has class 'c("terms", "formula")'.

_N_o_t_e:

     These objects are different from those found in S.  In particular
     there is no 'formula' attribute, instead the object is itself a
     formula.  Thus, the mode of a terms object is different as well. 

     Examples of the 'specials' argument can be seen in the 'aov' and
     'coxph' functions.

_S_e_e _A_l_s_o:

     'terms', 'formula'.

